Eddy current heating of rotors



g- 1951 A. B. WHITE ETAL 2,566,274

EDDY CURRENT HEATING OF ROTORS Filed June 13, 1947 2 Sheets-Sheet 1 ALL YN 5. WH/Tf B05587 15. JA(0B5 IN VEN TORS A TTOR/VE Y5 Aug. 28, 1951 A. B. WHITE ET AL 5 EDDY CURRENT HEATING OF RQTORS Fil ed June 13. 1947 2 Sheets-Shoe}: a

ALLY/V 5. WHITE &;

- 6 055,975. #1 .INVENTORS Q 2 BY in ,2 jciud d, fimlim 9 ATTORNEYS Patented Aug. 28, 1951 EDDY CURRENT HEATING OF BOTOBS Allyn B. White, Rochester, N. 2., and Robert E.

Jacobs, Chicago, 11L, assignors, by mesne assignments, to Eastman Kodak Company, Rochester, N. Y., a corporation. of' New Jersey Application June 13, 1947; Serial No. 754,510

Claims.

This invention relates toan improved method and apparatus for generating and controlling heat in a rotating metal member, and in particular to a centrifugal still wherein the rotor is heated by eddy currents induced in said rotor by a. magnetic field.

It has long been known that a magnetic field sets .up resistance to a conductor moving through it and that the additional force which must be exerted to move the conductor through the field is reflected in a heating effect within the conductor body. This effect-known as the eddy current effect-is best demonstrated by rotating an aluminum disk through the field of a permanent magnet or electromagnet. A resistance torque is set up by the magnetic field and the energy expended overcoming this torque is transferred into heat which warms the aluminum disk to a degree depending on thes-peedof rotation of the disk and the strength and con figuration of the magnetic field.

"This eddy current heating is normally an ob jectionable feature in electrical apparatus as it represents energy dissipationin the form of heat. Our invention contemplates the utilization of this eiieot as an efficient source of heat. In many applications eddy currents for heating are more efiicient than the source of heat normally used. For example, in Hickman Patents 2,308,008; 2,370,464; and 2,379,151 high vacuum centrifugal still apparatus are described wherein the rotors areheated by electrical resistance elements. In such apparatus the big disadvantage is that heat must radiate from the resistance element to the moving member. Therefore, the temperature of the heating element must be considerably above the temperature of the vaporizing surface and this results in significant .heat radiation losses, and possible vapor decomposition. With eddy current heating of the rotor radiation losses are held to a minimum.

This invention has for its object to provide improved method and apparatus for generating and controlling heat in a rotating metal member.

Another object is to provide improved method and apparatus for generating and controlling heat in a rotor in a vacuum. A further object is to provide improved method and apparatus for generating and controlling heat in a rotor in a vacuum for heating liquids. A. still further object is to provide improved method and apparatus for generating and controlling heat in a rotor in a vacuum for vaporizing liquids. Another object is to provide centrifugal distillation apparatus in which the vaporizing surface is heated by eddy currents. A further object is to provide a centrifugal still in which the rotation of the centrifugal surface induces eddy currents Whichmaintain the vaporizing surface at a uniform temperature. A still further object is to improve the state of the art. Other objects will appearhereinafter.

These and other objects are accomplished by our invention which includes a rotatable surface of a material of good electrical conductivity which is heated by eddy currents induced there-- inbya magnetic field positioned in the path of rotation of said rotatable surface. Our invention also includes means for controlling the magnitude and configuration of the magnetic field within which the rotatable surface moves.

In the following description we have given several of the preferred embodiments of our invention but it is to be understood that these are set forth for the purpose of illustration and not in limitation thereof.

In the accompanying drawings wherein like numbers refer to like parts:

Fig. 1 is a vertical section of a centrifugal still in which the magnetic field is provided by permanent magnets placed underneath the rotor, and heat is controlled by varying the gap between magnets and rotor;

-Fig. 2 is a sectional View of a rotor and permanent magnet design in Which leakage flux is largely eliminated by placing the rotor between the poles of horseshoe permanent magnets;

Fig. 3 is a sectional view of a rotor and magnets in which eddy currents are induced by electromagnets;

:Fig. 4 is a sectional view of a composite rotor with permanent magnets showing a method by which fiux leakage may be minimized;

Fig. 5 is a sectional view of a rotor and permanent magnet arrangement showing a method ofwincreasing the magnetic flux through which the rotor moves;

Fig. 6 is a view of one of the magnets, showing extensionpieces which may be attached to the poles to give a magnetic field of greater fiux density in the vicinity of the rotor;

.Fig. '7 shows an alternative method of varying the gap between the magnets and rotor. In this design the magnets (not shown) may be made stationary while the rotor may be raised or lowered;

Fig. 8 shows still another method of controlling the'magnetic field through which the rotor rotates;

-Fig. 9 is a sectional View of a massive rotor which may be heated by eddy currents;

' Fig. 10' is a sectional View of a rotor of the type used in large installations.

Referring to Figs. 1-5 and 7, 9, and 10 numeral l designates the rotatable vaporizing surface which is rotated by shaft H. In Figs. 1, 2, 4-6, 8, 9, and 10 numerals l2 designate permanent magnets which set up magnetic fields through which rotor Iii moves. For clarity magnets [2 are shown so that the observer sees the crescent in the drawings. In Figs. 2 and 5 this is the correct View for actual operation but in Figs. 1, l, 8, 9 and 10 magnets 12 are preferably rotated 90 in actual operation. We have discovered that the heating effect is enhanced if the poles of the magnets are parallel to the direction of rotation of rotor iii.

In Fig. l numeral It designates a cylindrical still casing provided with an integral baseplate M and a removable top plate i5 with which it makes a gas-tight contact by means of flange i6 and gasket ll. Top plate 15 is the condensing surface. Attached to rotor Hi is flange I8 to which is attached shaft i l. Shaft l I is housed in gas-tight bearing is and is provided with a driving pulley 2c. Numeral 2i designates an annular gutter which surrounds the periphery of rotor Ill to which gutter is connected the withdrawal conduit 25.. Numeral 23 indicates a conduit for introducing distilland onto the approximate center of rotor 15. Numeral 24 designates an annular channel integral with the upper inside wall of easing IS. Liquid collected in channet 24 is withdrawn by way of conduit 25. Numeral 26 designates an arm on which one or a plurality of permanent magnets may be rigidly fastened. For purposes of illustration only one arm is shown but more than one may be used. Numeral 21 designates a member which is fixedly attached to baseplate M. Numeral 23 designates a pivot or hinge which connects members 21 and 25. Numeral 29 designates a cylinder into which oil may be pumped through tube 30 to force upward shaft 3|, which impinges on member 26, thus closing the gap between magnets I 2 and rotor H Numeral 32 designates a coil spring in tension which serves to enlarge the gap between rotor I [l and magnets l2 when the oil pressure acting on cylinder 28 is decreased. Numeral 48 designates an evacuating conduit to Which vacuum pumps (not shown) may be connected when it is desired to operate as a still at less than atmospheric pressure.

In Fig. 2 numeral 33 designates a vertical member mounted so that it hinges on baseplate I 4. At the upper end of member 33 horseshoe magnet I2 is rigidly connected. Spiral tension spring 36. extends horizontally from the upper part of member 33 to still casing l3. Cylinder 35 is mounted on still casing i3. Shaft 36 extends from cylinder 35 to member 33 supporting horseshoe magnet !2. Tube 37 leads from cylinder 35 outside the casing Oil pressure exerted through tube 31 on cylinder 35 actuates shaft 36 against member 33 and in combination with tension spring 3% acts to control horseshoe magnet l2.

Referring to Fig. 3 the magnetic field through which rotor ill moves is formed by electromagnet 38. Heat supplied to the vaporizing surface is controlled by varying the exciting current flow-1 ing in the electromagnet. Referring to Fig. 4 numeral 39 designates a portion of the rotor constructed of a magnetic metal and numeral 40 designates a portion of the rotor composed of material of high electrical conductivity.

Referring to Fig. 5 rotor i0 is designed with concentric ridges l! which act to make maximum use of the magnetic flux.

Fig. 6 illustrates a method of increasing the flux density of that part of the magnetic field in which the rotor moves. Pole pieces 42 are attached to magnet l2. These pole pieces must be constructed of a magnetic material and may be a continuation of the magnet itself. They then have the property of concentrating the lines of magnetic flux in the path of rotor l0.

Fig. 7 illustrates a method of controlling the magnetic field intercepting the rotating member. Collar 43 on shaft H is utilized to raise or lower rotor ID by means of lever arm 44 on fulcrum support 45, thus changing the magnet-rotor spacing.

Fig. 8 illustrates still another method of controlling the strength of the magnetic field. Numeral 46 designates a bar composed of magnetic material which is placed so that it is on one side of rotor I!) while magnet i2 is on the other side. Bar 46 acts to decrease the reluctance of the magnetic path so that more flux is cut by the rotation of rotor Hi. This bar also concentrates the lines of magnetic fiux into a smaller portion of the rotor. Bar 4-5 is attached to shaft 41 which may be turned to lessen the number of lines of magnetic flux which pass through rotor l0. Alternatively, bar 46 could be moved by shaft 41 to a different location in order to change the flux conditions.

Fig. 9 shows a type of rotor that will have a very uniform surface temperature due to massive construction.

Fig. 10 shows a rotor of a type used in large installations. This design has been used successfully in sizes up to a diameter of five feet across the top of the rotor.

In operating the apparatus illustrated in Fig. 1 shaft I I is rotated at the desired speed. The gap between magnets I2 and rotor I0 is adjusted by hydraulic pressure so that the amount of heat supplied maintains the proper vaporizing surface temperature. Distilland is introduced through conduit 23 and vaporization takes place upon the hot surface of rotor Ill. If the air gap is kept constant increasing the speed of the rotor will increase the surface temperature. If the rate of rotation of the rotor is kept constant, decreasing the gap increases the magnetic fiux through the rotor to give greater heating of rotor metal. If the magnetic field is created by an electromagnet as illustrated in Fig. 3 the air gap and rate of rotation may be kept constant and the magnetic field controlled by changing the current flowing through the magnetic coil.

Our invention is of particular advantage where it is desired to heat fluids within a vacuum such as is encountered in high-vacuum unobstructedpath distillation which is carried out at a pressure of less than approximately 0.1 mm. of mercury. The apparatus of Fig. 1 may be evacuated to a pressure of less than approximately 0.1 mm. of mercury through vacuum pumps (not shown) attached to evacuating conduit 48, and it then becomes a high-vacuum unobstructed-path still. vaporized material is condensed on cover l5 and collected in channel 24 for withdrawal through conduit 25.

The apparatus of Fig. 1 may be used as a heating device instead of a still. The gap between magnets and rotor is adjusted so that the surface temperature of rotor I0 is maintained below distillation temperature and at some desired intermediate temperature. The liquid to be heated is introduced through conduit 23. Centrifllgal action forces it over rotor II] to gutter 2! from which it is withdrawn by; conduit 22. This process 'very quickly. bringsthe liquid up to any desired temperature-and local overheating .is avoided;

With the permanent magnet-design of Figs. 1,2, 4; 5,. 8, 9, and 'we prefer'to use magnets which createa strongexternal magnetic field" of high flux density. We have found that satisfactory magnets may be'composed of. dispersion hardening'alloys 'such'as are described on page 9 and "following of-circuiar of the National'Bureau i of Standards 0448 entitled Permanent Magnets',ibyRaymond L. Sanfordissued Au-' gust'lo; 1944. With the design of Fig. 1 wehave generated as'much as 250"Watts' ofheat from 'a l-lbxm'agnet with a'M-inch diameter'aluminum rotor operated at 1750 R. PPM: Magnetsof lower strength may be 'used and'any magnet; however weak; will have someheating effect;

Thenumberof magnets used and'the type of control depends-on the "operating requirements.

One "large magnet may have the same heating. effect as a plurality oi' 'smaller' ones: We'hzive I of 1750 R. P. ML With :seven magnetsweighing a total' of '2 pounds 'we"have'attained surface temperature of 300" C; one '14 rotor "rotating at 1750-R.-P; M;

The speedof rotation of -the rotonisusually" fixed-and-thi's necessitates regulating the: rotor" temperature 'by changing: the" magnetic field,

such-'asby changing th'e gap between the rotorand magnets; Fig. 1 showsa-simplemethod by which thi's is achieved. The oil pressurer'in' cylinder 22 is controlled by an external plunger (not shown) operating on line 301- Forcingt'th'e' external plunger actuatesl shaft 3| 'and raises membenzfi, closing the gap between rotor I0 and magnets"l2.' Releasing the'plunger enables tension spring-'32 to pull memberZB away'from" rotor -l 9 thus widening 4 the gap between' roto'r 2| it andni'agnets li In the design'of Figfizmagneti'm flux is more fully utilized by having the-two poles of the magnets straddle rotor 'lfii In -Fig-3 the magnetic: field is prOVide'cP by electromagnets.

Where the installation isunder high vacuum the dissipation of heat from ith'e fl electromagnetsis very slow and the magnet miust be cooled.-

Figl i'shows a rotor of compositeconstructionl Rotors constructed of metals of high electrical? conductivity such as aluminum;

num or similar conducting metalie placed be-' copper,- and i silver'are more" easily heated by eddyficurren We have utilized the' fact that if a'disk of alumi tween the magnet's -and' a disk of iron or similar? magnetic material; I the: magnetic 'di'slc' increase's' andconcentr'ates the magnetic field through the" rotor; thus increasing the heating effect Fig..'5 shows another method of increasing the' effectiveness of the magnets? Rotor lfl is designed with 'concentric' ridges Al which rotate between the poles of the horseshoe permanent magnets. The flux passes through these ridges 5 givinga more pronounced'heating 'eflTe'ct.

Fig. 6 demonstrates a method ofimproving the effectiveness of the "magnets- The -pole-pieces are' extensions of I the "magnet which nee'd not be constructed of the. same materialas the:

net but which must-"be-ofwmagneticxmaterial;

such as iron. These pieces" extend upward I toward one another at an angle of about 45 serve to concentrate the lines of magnetic-flux with minimum leakage so that more of thempass through a small part of the rotor.

netic field-isconcentrated by having a small left between the poles;

gap between magnet and rotor allows'for con siderable "leakage flux:

In Fig-7 the magnets (not shown) arefixedly.

attached to the bodyof theapparatus'in' a position-- immediately adjacent to the rotor. The

lever arm is then used to "raise or lower the rotorto control the strength and size of themagnetic' field through the rotor.

In Fig. 8 the bar of magnetic material above the -rotor concentrates the magnetic flux in a manner'similar to the design illustrated in Fig; 4. Any j'control'means which moves this bar to a position where it concentrates less magnetic flux will enable the rotorto operate at a lower. temperature; tendency to heat up it may form part of a con densing surface.-

Table I shows the effect on the heat generated of changing the gap between rotor and magnets.

The rotor used was made of aluminum thick "by 14%" diameter. The'rate of rotation was 1750 R. P. M.

Table. I

sip tar Inches Watts A2 200 Vic- Y 185 is 150 Mi is so Anelectromagnet of constant strength was used in securing the above data.'

Table II' shows the effect of velocity on op mum rotor thickness.

Table .II

Radius Linear Rotor at Velocity" Heating Velocity Magnet at 1G Effect Position Magnet Hess R. PyM Inches FL/sec. Inches Watts 840' 6 .44 As 80 840 6 44 M; S40 6 44 1 /4 840;- 6 44 it 115 1,490 6 H 78 m, 180 1,490 6 78 1 i 290 1. 490- 6 I 78 $4 270 l. 750 4% 72. 5 M6 7 1,750 4%. 72.5 1 160. 1,750 v 4%, 72. 5. /4 140. l, 750 4% 721 5 100' 1, 750 4% 72. 5 1 95 2, 540. 6 I 105 1 A6 610. 2. 540 I") 105 A 520 2. 540 6 105 M 410 1 Indicates approximate optimum thickness.-

The test from whichthei above dat'aiare taken: was run'withfaluminum IOtOTS OfT14i /Q diameter; An "electromagnet "of constant strength was used I They If'the gap between the rotor and magnets is small themag Since the magnetic bar itself has no in securing the above data and the gap between rotor and magnet was constant.

The heating eifect of the eddy currents depends on the number of lines of magnetic flux being cut per unit of time and the distribution of these lines in the rotor. Rotor characteristics which affect this are the diameter and thickness of the rotor, the electrical conductivity of the material from which the rotor is made, and rate at which the rotor is rotating through the magnetic field. Factors which affect the strength of the magnetic field are the design of the magnets, the material from which the magnets are constructed, the degree of magnetization, the gap between the magnets and rotor, the configuration of the magnets with respect to the rotor, and the presence or absence of flux directing materials in the vicinity of the magnetic field. It is obvious that there may be variations in any of the above factors without departing from the scope of our invention.

What we claim is:

l. Centrifugal vacuum distillation apparatus comprising an enclosed still chamber, means for evacuating said chamber, a generally conical metal rotor rotatably mounted in said chamber, the concave surface of said rotor being a vaporizing surface, means for introducing distilland onto said concave surface of said conical rotor, means for rotating said rotor at a speed effective to centrifugally move distilland across said rotor, stationary condensing means separated from said rotor by substantially unobstructed space, and a plurality of stationary magnets disposed in said chamber substantially adjacent to said rotor, the poles of said magnets being disposed substantially adjacent to a surface of said conical rotor other than said vaporizing surface, said rotor being disposed in the magnetic field of said magnets and being arranged for cutting the lines of magnetic force of said magnets during rotation of said rotor, said magnets constituting essentially the sole means for heating said rotor.

2. Centrifugal vacuum distillation apparatus comprising an enclosed still chamber, means for evacuating said chamber, a generally conical metal rotor rotatably mounted in said chamber, the concave surface of said rotor being. a vaporizing surface, means for introducing distilland onto said concave surface of said conical rotor, means for rotating said rotor at a speed effective to centrifugally move distilland across said rotor,

stationary condensing means separated from said rotor by substantially unobstructed space, a plurality of stationary magnets disposed in said chamber substantially adjacent to said rotor, the poles of said magnets being disposed substantially adjacent to a surface of said conical rotor other than said vaporizing surface, said rotor being disposed in the magnetic field of said magnets and being arranged for cutting the lines of magnetic force of said magnets during rotation of said rotor, said magnets constituting essentially the sole means for heating said rotor, and adjusting means operable from outside said chamber for moving said magnets toward and away from said rotor.

3. Centrifugal vacuum distillation apparatus comprising an enclosed still chamber, means for evacuating said chamber, a generally conical metal rotor rotatably mounted in said chamber, said rotor having an upwardly directed concave vaporizing surface, means for introducing distilland onto a central zone of said vaporizing surface of said rotor,'means for rotating said rotor at a speed effective to centrifugally move the dis-- tilland across said vaporizing surface to the periphery of said rotor, stationary condensing means in said chamber separated from said vaporizing surface by unobstructed space, a plurality of stationary magnets mounted in said chamber below said rotor, the poles of said magnets being disposed substantially adjacent to said rotor, said rotor being disposed in the magnetic field of said magnets and being arranged for cutting the lines of magnetic force of said magnets during rotation of said rotor, and adjusting means operable from outside said chamber for moving said magnets toward and away from said rotor, said magnets constituting essentially the sole means for heating said rotor.

4. Centrifugal vacuum distillation apparatus comprising an enclosed still chamber, means for evacuating said still chamber to a pressure below 0.1 mm. of mercury; a generally conical metal rotor disposed in said still chamber, said rotor including a generally concave vaporizing surface, means mounting said rotor for rotation Within said chamber with said vaporizing surface directed generally upwardly, means for introducing distilland onto a central zone of said vaporizing surface of said rotor, means for rotating said rotor at a speed effective to centrifugally move the distillate across said vaporizing surface to the periphery of said rotor, a stationary annular gutter extending around the periphery o said rotor and being constructed and arranged for collecting undistilled distilland from the periphery of said rotor, stationary condensing means separated from said vaporizing surface by substantially unobstructed space and being constructed and arranged for condensing vapors distilling from said vaporizing surface, and a plurality of stationary magnets mounted in said chamber below said rotor, the poles of said magnets being substantially adjacent to said rotor, said magnets being disposed with the paired poles of each said magnet generally parallel to the path of rotation of said rotor, said rotor being disposed in the magnetic field of said magnets and arranged to cut the lines of magnetic force during rotation of said rotor, said magnets constituting essentially the sole means for heating said rotor.

5. Centrifugal vacuum distillation apparatus comprising an enclosed metal still chamber, means for evacuating said still chamber to a pressure below 0.1 mm. of mercury, a rotatable shaft extending into said chamber through the bottom I of said chamber, a generally conical aluminum rotor mounted on said shaft in said chamber, said rotor having a generally upwardly directed concave vaporizing surface, means for introducing distilland onto a central zone of said vaporizing surface, means for rotating said shaft and rotor at a speed effective to centrifugally move distilland across said vaporizing surface from said central zone to the periphery of said rotor, stationary metal condensing means spaced from said 9 10 magnets and being arranged for cutting the lines REFERENCES CITED of magnetic force of Said magnets during rota The following references are of record in the tion of said rotor. said magnets constituting esfile of this patent: sentially the sole means for heating said rotor, and adjusting means extending through a wall 5 UNITED STATES PATENTS of said chamber and operable from outside said Number Name Date chamber, said adjusting means being constructed 1,507,686 Root Sept. 9, 1924 and arranged for moving said magnets toward 1,912,214 Northrup May 30, 1933 and away from said rotor during operation of 2,000,155 White May 7, 1935 said apparatus. 10 2,181,921 Schlup Dec. 5, 1939 ALLYN B- WI-H 2,188,569 Endsley Jan. 30, 1940 ROBERT B. COB 2,224,621 Voorhees Dec. 10, 1940 2,308,008 Hickman Jan. 12, 1943 2,313,175 Scott et a1 Mar. 9, 1943 

